On saying “Enough already!” in SQL

Abstract

In this paper, we study a simple SQL extension that enables query writers to explicitly limit the cardinality of a query result. We examine its impact on the query optimization and run-time execution components of a relational DBMS, presenting two approaches—a Conservative approach and an Aggressive approach—to exploiting cardinality limits in relational query plans. Results obtained from an empirical study conducted using DB2 demonstrate the benefits of the SQL extension and illustrate the tradeoffs between our two approaches to implementing it.